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Date: Thu, 26 Oct 89 16:49:06 CDT
From: keenan@tartarus.UChicago.EDU (Philip Keenan)
Message-Id: <8910262149.AA15018@tartarus.uchicago.edu>
To: bugs@tartarus.uchicago.edu
Subject: Another bug in GNU C++
Cc: keenan@tartarus.uchicago.edu


Here is another bug you can forward to the GNU people. It is an
especially nasty and subtle one, where something internal has
the wrong value, but when you print the value to check, the act
of printing gets rid of the bug, so it prints the correct value,
leaving you to wonder why it fails when you comment out the print line!

- -- Phil Kenan

***************************************************************
/* bug.cc

   Phil Keenan 10-25-89.

   This short program illustrates a bug in GNU C++ v. 1.35.1-

   As it stands, it produces as output "0" and "1", which is incorrect.
   They should both be "1".
   If you simply uncomment the commented out line in function complex::cabsv(),
   it does compute them correctly.

*/

#include <stream.h>

double absv(double d) { if(d>=0) return d; else return -d; }

struct complex {
  double r, i;
  complex(double re=0, double im=0) { r=re; i=im; }
  double cabsv();
};

double complex::cabsv()
{
  double x,y;
  x = absv(r);
  y = absv(i);
//  cout << x << " " << y << "\n";
  if(x==0.0) return y;
  if(y==0.0) return x;
  return 100;
}

void main()
{
  complex e;
  e = complex(0,1);
  cout << e.cabsv() << "\n";
  e = complex(1,0);
  cout << e.cabsv() << "\n";
}
***************************************************************
The end.

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